Barrel Tip Deflection

[ThunderDownUnder]

If you have trouble sleeping at night then I suggest you read the tech article on using neural networks to calculate barrel tip deflection.

It seems its possible to calculate the barrel tip deflection caused by the projectile, (moving mass) at least for military purposes and examples used were for 35mm anti-aircraft rounds and barrels.

I'm sure it could be adapted to be used on target barrels as well.

It certainly makes clear to me the importance of matched mass and velocity of the projectiles we use!

Enjoy

http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1679-78252016001001968
https://www.researchgate.net/public..._MM_ANTI-AIRCRAFT_CANNON_BARREL_DURING_FIRING

 

[dcali]

A bit complex for my taste, but clever.

 

[Mr.Knowit all]

WOW!! I haven't seen that many numbers on a page since college. That just sounds like another name for "barrel whip". Anyone else get that impression?

 

[dcali]

WOW!! I haven't seen that many numbers on a page since college. That just sounds like another name for "barrel whip". Anyone else get that impression?

That's exactly what it is. It's an attempt at quantifying it, though, which is not easy.

 

[JRS]

Does it really matter? The barrel vibrates much in the same way a guitar string does after the string is plucked/released, or the vibration felt on a bow after the arrow has been released, or the deflection (paradox) of an arrow after it leaves the string.

 

[dcali]

Does it really matter? The barrel vibrates much in the same way a guitar string does after the string is plucked/released, or the vibration felt on a bow after the arrow has been released, or the deflection (paradox) of an arrow after it leaves the string.

It matters because the force driving the vibration starts immediately as the trigger is pulled, starting with the firing pin impact (which is measurable even without a charge - I think this may be what people are tuning when they start messing around with ignition, at least in part). So the barrel vibrates before the bullet leaves the barrel.

 

[JRS]

It matters because the force driving the vibration starts immediately as the trigger is pulled, starting with the firing pin impact (which is measurable even without a charge - I think this may be what people are tuning when they start messing around with ignition, at least in part). So the barrel vibrates before the bullet leaves the barrel.

Does a tuning fork vibrate as you strike it, or after you remove it from the surface you strike it against?

 

[dcali]

Does a tuning fork vibrate as you strike it, or after you remove it from the surface you strike it against?

When you strike the fork, it bends while still in contact with whatever you hit. The speed with which it starts vibrating depends on the speed of sound in the material, which for steel is extremely fast - about 20,000 feet per second. That's as fast as any deflection can move through a material. Think of it as a wave moving through the material - one end of the fork can't know the other end has been struck until that wave travels across, at the speed of sound in steel.

So as soon as that wave can propagate through the fork, it is technically vibrating. It's vibrating in a way that's influenced by the fact that there is still contact with the fork, but it's still vibrating. Once you remove the contact, the frequency will change and it will continue to vibrate until it damps out. Notice the "tink" that you hear when you strike the fork. That's the sound generated by the initial vibration. Also notice that it's not the same pitch as the fork's free vibration.

You have to think of vibration as a dynamic motion rather than a constant sine wave. It's more whip than tuning fork.

 

[boltfluter]

Alex Wheeler is doing some great work in this area. It does make one take a step back, and put on the old thinking cap.Good stuff that we will all benefit from. Thanks Alex.

Paul

 

[JRS]

Too much overanalyzing taking place.

 

[dcali]

I disagree. This is exactly how tuning a rifle works. It's the difference between a 1/2 MOA rifle and a 2 MOA rifle. Understanding this allows us to manipulate it.

 

[JRS]

I disagree. This is exactly how tuning a rifle works. It's the difference between a 1/2 MOA rifle and a 2 MOA rifle. Understanding this allows us to manipulate it.

Personally, I believe most of it comes down to the array of better barrels, bullets, tuners, and the time our better shooters are willing to sacrifice at the bench. Compared to today, the small group record that stood for more than 4 decades was set using much less expensive equipment than we use today, the rifle was not topped off with a 60x $2000.00 scope, the barrel wasn't clocked to a certain position, and B&A triggers didn't exist, and the cartridge was the 222 Remington fired in a button rifled barrel. At some point, hard work and commitment pays off.

Edit: I'd be willing to bet a dollar to donuts that some of our older shooters could pull out their ancient BR guns and shoot just as small as they do with their current/modern guns. A great deal of what we pay for now is more a matter of luxury and want, rather than necessity. The difference between winning and second place comes down to hard work, commitment and Lady Luck.

 

[mgunderson]

The problem gets complex when you talk about the stock and how it interacts with the supports and/or the human body. I also believe Alex is doing some interesting work.

Varmint Al has some interesting models on his web page that looked at tuners.

 

[normmatzen]

Soon as the gun fires, a longitudinal resonance is formed. When the bullet exits the muzzle with respect to the node of this resonance determines the ES of a group. When the bullet tries to fly straight down the barrel, it causes a vertical resonance, or cantilever. This is where you want to tune the barrel so the muzzle points the correct angle to make the bullet hit mid X!

That's why I test the barrel with round robin 5 shot groups with a series of loads. Best ES as evaluated by Excel and curve fitting tells me the exact load. Then after loading that "perfect" load, I take off the MagnetoSpeed and screw on the tuner weight and do 2-3 shot groups as I adjust the tuner over maybe 0.1" with 1/80" increments.

And, the correct jump just happens to be at what ever jump I used for the round robin load determination. And, yes, I tried many times to improve with adjusting jump with no success.

Disclaimer: This can't make a bad barrel shoot great. just allows a good barrel to shoot its best.
And, Yes, you can replace all this by ladder testing and jump adjusting and get the same result.

 

[dgeesaman]

Does a tuning fork vibrate as you strike it, or after you remove it from the surface you strike it against?

Both.

 

[Ned Ludd]

It matters because the force driving the vibration starts immediately as the trigger is pulled, starting with the firing pin impact (which is measurable even without a charge - I think this may be what people are tuning when they start messing around with ignition, at least in part). So the barrel vibrates before the bullet leaves the barrel.

If the last inflection point (node) of barrel vibration is known, the ability to accurately estimate barrel tip deflection would also allow one to make a pretty good estimate of muzzle launch angle. Together, those two values would be pretty useful for predictive in silico load development estimates. Certainly one can always simply load rounds and put holes in paper to achieve the same goal, but I've always believed that predictive tools such as QuickLoad can expedite the process considerably when used correctly.

 

[Papa Charlie]

While the math is over my head. When you read the conclusion, it is clear that there are three things that create variation and they sum it up with this sentence:

"The most important parameters affecting a weapon system's dynamics are the projectile-mass, acceleration, and exit velocity."

and we already know to try and control these through bullet lot numbers and sorting, using the same lot number of powder and accurate measurement of the powder load.

 

[Bart B.]

Use these to see why the muzzle doesn't point to a place above point of aim equal to sight height plus bullet drop when the primer fires:

http://www.geoffrey-kolbe.com/articles/rimfire_accuracy/tuning_a_barrel.htm

http://www.geoffrey-kolbe.com/articles/rimfire_accuracy/barrel_vibrations.htm

https://www.varmintal.com/ashot.htm. (links to barrel tuners, harmonics)

Mechanical engineers (Al Harral, Geoffrey Kolbe) in vibration disciplines have proved the fundamental (lowest) frequencies barrels vibrate at are a few dozen cycles per second. There's several harmonics at higher frequencies up to around 8 to 9 thousand cycles per second. The 3rd harmonics near 800 to 1000 Hz are the ones barrel tuners usually work in.

The speed of sound in barrel steel is about 16,000 to 19,000 cycles per second.

Here's a century + old article about positive compensation the 303 British is noted for:

https://ia800701.us.archive.org/6/items/philtrans05900167/05900167.pdf

Most important is understanding that tuners moving back and forth near barrel`s muzzle change the frequency the muzzle axis moves vertically on the upswing so slower bullets leave at greater angles to the LOS than faster ones to positively compensate for their greater drop at target range.

Most of the muzzle axis swing is vertical because the rifle's recoil force axis is above the center of mass (rifle and what's holding it).

 

[Bart B.]

Certainly one can always simply load rounds and put holes in paper to achieve the same goal, but I've always believed that predictive tools such as QuickLoad can expedite the process considerably when used correctly.

In my two phone conversations with Quickload's rep, I learned that any one of their loads can produce near 100 fps difference between its calculated data and what ones combination of components, bullet release force, rifle hold and dimensions of bore and bullet produce. Quickload calculates trends in data numbers, not what you will produce with your stuff.

No wonder arsenals had a 2 or more grain spread in IMR4895 average charge weights across all lots meeting 30-06 and 7.62 ammo accuracy, velocity and pressure specs. Charges had about 3/10 grain spread in a given lot.

 

[mongo chicago]

Makes one wonder how anybody ever shot accurately before knowing this.